Insulators are generally used to secure, mount or support first current or voltage-carrying assemblies on or in second assemblies, such as housings, frames, supports, etc., when a current flow between the first current or voltage-carrying assembly and the second assembly is to be prevented.
For safety reasons a defined insulation resistance of the insulator must often be ensured in this process. For example in the case of an electrical device supported in a housing or vessel, e.g. in the case of a fuel cell module supported in a pressure vessel, a high insulation resistance must be ensured between the housing or vessel and the electrical terminals of the device. The electrically conducting parts of the device are therefore connected to the housing or vessel by way of insulators for securing, mounting or supporting purposes. In the case of some installations or devices the insulation resistance between the housing or vessel and the electrical terminals is permanently monitored and the installation or device is disconnected if the value of said insulation resistance drops below a limit value.
If insulators are in an environment where the temperature changes from hot to cold, as the environment cools moisture in the ambient atmosphere condenses and is deposited on the insulators. The deposited moisture forms water drops on the insulators and these join up to form a film of water wetting the surface. This produces electrically conducting water bridges assemblies to be insulated, which can cause the insulation resistance to be reduced by a factor of 10 or more for example.
For safety reasons the insulation sections are therefore generally designed to be so long that the sections of water do not significantly reduce the insulation resistance.
Further measures for preventing insulation resistances being too low are to prevent the condensation of moisture by drying the atmosphere with the aid of a drying facility or by not permitting operation of the device in the cold state.